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AS2954
250 mA Low Drop Out Voltage Regulator
FEATURES
* Output Accuracy 5V, 3.3V,@ 250mA Output * Very Low Quiescent Current * Low Dropout Voltage * Extremely Tight Load And Line Regulation * Very Low Temperature Coefficient * Current & Thermal Limiting * Improved Replacement With Hight IOUT For LP2954 Sockets
APPLICATIONS
* Battery Powered Systems * Cordless Telephones * Radio Control Systems * Portable/Palm Top/Notebook Computers * Portable Consumer Equipment * Portable Instrumentation * Automotive Electronics * SMPS Post-Regulator * Voltage Reference * Avionics
AS2954 Version Over LP2954
* Error Flag Warns Of Output Dropout * Logic-Controlled Electronic Shutdown * Output Programmable From 1.24V to 29V * Input Can Withstand -20V Reverse Battery & +60 Positive Transient
PRODUCT DESCRIPTION
The AS2954 is a low power voltage regulator. This device is an excellent choice for use in battery-powered applications such as cordless telephones, radio control systems, and portable computers. The AS2954 features very low quiescent current (75A Typ.) and very low dropout voltage. This includes a tight initial tolerance of 0.5% max and 1% max., and very low output temperature coefficient, making the AS2954 useful as a low-power voltage reference. The key AS2954 features include protection against reversed battery, fold-back current limiting, and automotive load dump protection (60V positive transient). The error flag output feature is used as power-on reset for warning of a low output voltage, due to falling voltage input of batteries. Another feature is the logic compatible shutdown input which enables the regulator to be switched on and off. The AS2954 is offered in a 3-pin TO-92and TO-263 package compatible with other 5 volt regulators, in 8-Pin plastic, SO-8, (same pin out as AS2951), TO220 and TO-263. The regulator output voltage (of the 8-pin) may be pin-strapped for a 5Vand 3.3V or programmed from 1.24V to 29V with an external pair of resistors. Look for AS2951 for 150mA and LP2951 for 100mA applications.
PIN CONNECTIONS
TO-263-3 Package TO-263-5 Package
8-Pin Surface Mount (S)
OUTPUT 1 2 3 4 AS2954 8 7 6 5 INPUT FEEDBACK 5V, 3.3V TAP ERROR
1
SOT-223 Package
TO-220-3 Package
TO-220-5 Package
AS2954 1 2 3
AS2954 1 2345 1) INPUT 2) 3) 4) 5) OUTPUT GND SHUTDOWN ERROR
SENSE SHUTDOWN GND
AS2954
2 3
AS2954
AS2954 1) INPUT 2) OUTPUT
Top View
TO-92 (N) 1 2 3
V IN
GND
VOUT
3) GND 4) SHUTDOWN 5) ERROR 123 VIN GND VOUT 1 234 5
Front View
VADJ VOUT
VIN
Top View
Top View
Front View
OUTPUT GND INPUT
Front View
Bottom View
Rev.9/29/00
AS2954
ORDERING INFORMATION
TO-263 3-PIN AS2954YT3-X TO-263 5-PIN AS2954YT5-X TO-92 3 PIN AS2954YN-X TO-220 3 PIN AS2954YU3-X TO-220 5 PIN AS2954YU5-X PLASTIC SOIC 8 PIN AS2954YS-X SOT-223 3 PIN AS2954YM3-X OPER.TEMP. RANGE -40C to +125C
X= Output Voltage: (3.3 for 3.3V, 5.0 for 5.0V) Y= Output Tolerance (A = 0.5%, Blank = 1%; B = 2%)
ABSOLUTE MAXIMUM RATINGS
Power Dissipation..........................................Internally Limited Lead Temp. (Soldering, 5 Seconds) ................................ 260C Storage Temperature Range ............................ -65 to +150C Operating Junction Temperature Range (Note 9) AS2954 .................................................. -40C to +125C Input Supply Voltage .......................................-20V to +60V Feedback Input Voltage .....................................-1.5 to +30V Shutdown Input Voltage.....................................-0.3 to +30V Error Comparator Output ...................................-0.3 to +30V ESD Rating ............................................................ 2KV Min
ELECTRICAL CHARACTERISTICS at VS=15V, TA=25C, unless otherwise noted. Boldface applies over the full
operating temperature range.
Parameter 3.3V Version Output Voltage Conditions Typical AS2954A Min Max 3.284 3.267 3.260 3.251 3.317 3.333 3.340 3.350 AS2954 Min Max 3.267 3.251 3.234 3.201 3.333 3.350 3.366 3.399 AS2954B Min Max 3.234 3.201 3.194 3.168 3.366 3.399 3.432 3.432 Units
Output Voltage 5V Version Output Voltage
TJ =25C -25C TJ +85C -40C TJ +125C 1mA IL 250mA TJ TJMAX TJ =25C -25C TJ +85C -40C TJ +125C 1mA IL 250mA TJ TJMAX
3.3
V
3.3
V
Output Voltage All Voltage Options Output Voltage Temperature Coefficient Line Regulation (Note 3) Load Regulation (Note 3) Dropout Voltage (Note 5)
5.0 5.0 5.0 5.0
4.975 4.95 4.94 4.925
5.025 5.050 5.06 5.075
4.95 4.925 4.90 4.85
5.05 5.075 5.10 5.15
4.90 4.85 4.84 4.80
5.10 5.15 5.20 5.20
V
V
20 (Note 1) 6V VIN 30V (Note 4) IL = 1 to 250 mA IL = 0.1 to 1 mA IL = 1mA IL = 50mA IL= 100mA IL= 250 mA 0.03 0.04 60 220 250 375 90 1 4.5 21
100 0.10 0.20 0.16 0.20 100 150 250 420 300 450 450 600 150 180 2 2.5 6 8 14 16 550 600 0.2
150 0.20 0.40 0.20 0.30 100 150 250 420 300 450 450 600 150 180 2 2.5 6 8 20 22 550 600 0.2
180 0.40 0.60 0.30 0.40 100 150 250 420 300 450 450 600 150 180 2 2.5 6 8 26 28 550 600 0.2
ppm/C %max %max mV
Ground Current
IL = 1mA IL = 50mA IL = 100mA IL = 250 mA
A mA
Current Limit Thermal Regulation Output Noise, 10Hz to 100khz IL = 100mA 8-Pin Versions only Reference Voltage Reference Voltage Feedback Pin Bias Current Reference Voltage Temperature Coefficient Feedback Pin Bias Current Temperature Coefficient
VOUT = 0 0.05 CL = 2.2F CL = 33 F 400 260 Typical 1.235
mA %/w V rms
Over Temperature (Note 6) 20
AS2954A 1.220 1.250 1.200 1.260 1.190 1.27 40 60
AS2954 1.210 1.200 1.185 1.260 1.270 1.285 40 60
AS2954B 1.200 1.270 1.190 1.280 1.180 1.295 40 60
V V nA ppm/C
(Note 7)
50 nA/C 0.1
Rev.9/29/00
AS2954
(Continued)
Parameter Conditions (Note 2) Typical AS2954A Min Max AS2954 Min Max AS2954B Min Max Units
Applies for AS2954YT5-X, AS2954YU5-X and AS2954YS-X Error Comparator Output Leakage Current Output Low Voltage Upper Threshold Voltage Lower Threshold Voltage Hysteresis Shutdown Input VSD Hysteresis(HYST) Input Bias Current(IB) VIN(SD) = 0V to 5V VOH = 30V VIN = 4.5V IOL = 400A (Note 8) (Note 8) (Note 8) 0.01 150 240 350 60 -320 -380 -450 -640 100 2.00 250 400 -150 -100 230 160 -320 -380 -450 -640 100 2.00 250 400 -150 -100 230 160 -320 -380 -450 -640 100 2.00 250 400 -150 -100 230 160 A mV mV mV mV
Output Turn-On Threshold Voltage 6 10
1.155 1.140
1.305 1.320
1.155 1.140
1.305 1.320
1.155 1.140
1.305 1.320
V mV nA
-30 -50
-30 -50
-30 -50
-30 -50
-30 -50
-30 -50
Note 1: Output or reference voltage temperature coefficients defined as the worst case voltage change divided by the total temperature range. Note 2: Unless otherwise specified all limits are guaranteed for TJ = 25C, VIN = 6V, IL = 100 A and CL = 1F. Additional conditions for the 8-pin versions are feedback tied to 5V tap and output tied to output sense (VOUT = 5V) and VSHUTDOWN 0.8V. Note 3: Regulation is measured at constant junction temperature, using pulse testing with a low duty cycle. Changes in output voltage due to heating effects are covered under the specification for thermal regulation. Note 4: Line regulation for the AS2954 is tested at 150C for IL = 1 mA. For IL = 100A and TJ = 125C, line regulation is guaranteed by design to 0.2%. See typical performance characteristics for line regulation versus temperature and load current. Note 5: Dropout voltage is defined as the input to output differential at which the output voltage drops 100 mV below its nominal value measured at 1V differential at very low values of programmed output voltage, the minimum input supply voltage of 2V (2.3V over temperature) must be taken into account. Note 6: VREF VOUT (VIN - 1V), 2.3 VIN30V, 100AIL 250 mA, TJ TJMAX. Note 7: Comparator thresholds are expressed in terms of a voltage differential at the feedback terminal below the nominal reference voltage measured at 6V input. To express these thresholds in terms of output voltage change, multiply by the error amplifier gain = VOUT/VREF = (R1 + R2)/R2. For example, at a programmed output voltage of 5V, the ERROR output is guaranteed to go low when the output drops by 95 mV x 5V/1.235 = 384 mV. Thresholds remain constant as a percent of VOUT as VOUT is varied, with the dropout warning occurring at typically 5% below nominal, 7.5% guaranteed. Note 8: VSHUTDOWN 2V, VIN 30V, VOUT =0, feedback pin tied to 5V Tap. Note 9: The junction -to-ambient thermal resistance of the TO-92 package is 180C/ W with 0.4" leads and 160C/ W with 0.25" leads to a PC board. The thermal resistance of the 8-Pin DIP package is 105C/W junction-to-ambient when soldered directly to a PC board. Junction-to-ambient thermal resistance for the SOIC (S) package is 160C/W.
UNREGULATED DC 7 FEEDBACK 8 INPUT 1 OUTPUT 2 SENSE + _ FROM CMOS OR TTL 3 SHUTDOWN 60k .. 180k .. 6 ERROR AMPLIFIER 5V TAP + 1F ..
VO 5V @ 250mA MAX
+
330k ..
+
60 mV + 1.23V
+ _ ERROR COMPARATOR
5 ______ ERROR
TO CMOS OR TTL 4
REFERENCE GROUND
AS2954 Block Diagram
Rev.9/29/00
AS2954
APPLICATION HINTS
EXTERNAL CAPACITORS
For the stability of the AS2954 requires a 2.2F or greater capacitor between output and ground. Oscillation could occur without this capacitor. Most types of tantalum or aluminum electrolytic works fine here. For operations of below -25C solid tantalum is recommended since the many aluminum types have electrolytes the freeze at about -30C. The ESR of about 5 or less and resonant frequency above 500kHz are the most important parameters in the value of the capacitor. The capacitor value can be increased without limit. At lower values of output current, less output capacitance is required for stability. For the currents below 10mA the value of the capacitor can be reduced to 0.5F and 0.15F for 1mA. More output capacitance needed for the 8-pin version at voltages below 5V since it runs the error amplifier at lower gain. At worst case 5F or greater must be used for the condition of 250mA load at 1.23V output. The AS2954, unlike other low dropout regulators will remain stable and in regulation with no load in addition to the internal voltage divider. This feature is especially important in application like CMOS RAM keep-alive. When setting the output voltage of the AS2954, a minimum load of 1A is recommended If there is more than 10 inches of wire between the input and the AC filter capacitor or if a battery is used as the input then a 1A tantalum or aluminum electrolytic capacitor should be placed from the input to the ground. Instability can occur if there is stray capacitance to the AS2954 feedback terminal (pin 7). This could cause more problems when using a higher value of external resistors to set the output voltage. This problem can be fixed by adding a 100pF capacitor between output and feedback and increasing the output capacitor to at least 3.3F.
ERROR DETECTION COMPARATOR OUTPUT
The Comparator produces a logic low output whenever the AS2954 output falls out of regulation by more than around 5%. This is around 60mV offset divided by the 1.235 reference voltage. This trip level remains 5% below normal regardless of the programmed output voltage of the regulator. Figure 1 shows the timing diagram depicting the ERROR signal and the regulator output voltage as the AS2954 input is ramped up and down. The ERROR signal becomes low at around 1.3V input, and goes high around 5V input (input voltage at which VOUT = 4.75. Since the AS2954's dropout voltage is load dependent, the input voltage trip point (around 5V) will vary with the load current. The output voltage trip point (approx. 4.75V) does not vary with load. The error comparator has an open-collector output, which requires an external pull-up resistor. Depending on the system requirements the resistor may be returned to 5V output or other supply voltage. In determining the value of this resistor, note that the output is rated to sink 400A, this value adds to battery drain in a low battery condition. Suggested values range from 100K to 1M. If the output is unused this resistor is not required.
PROGRAMMING THE OUTPUT VOLTAGE OF AS2954
The AS2954 may be pin-strapped for 5V using its internal voltage divider by tying Pin 1 (output) to Pin 2 (sense) and Pin 7 (feedback) to Pin 6 (5V Tap).
+VIN
4.75V 100K OUTPUT VOLTAGE _______ ERROR* ERROR OUTPUT 5 ______ ERROR
8 +VIN VOUT 1 1.2 to 30V
AS2954
SHUTDOWN INPUT 3 SD GND 4 FB 7 1.23V R1 .01uF + 3.3uF
+5.0V
INPUT VOLTAGE
+1.3V
+ +
V REF
R2
* See Application Info.
_______ Figure 1. ERROR Output Timing
Figure 2. Adjustable Regulator
Rev.9/29/00
AS2954
Also, it may be programmed for any output voltage between its 1.235V reference and its 30V maximum rating. As seen in Figure 2, an external pair of resistors is required. Refer to the below equation for the programming of the output voltage: VOUT = VREF x ( 1 + R1\ R2 )+ IFBR1 The VREF is 1.235 and IFB is the feedback bias current, nominally -20nA. The minimum recommended load current of 1A forces an upper limit of 1.2 M on value of R2. If no load is presented the IFB produces an error of typically 2% in VOUT, which may be eliminated at room temperature by trimming R1. To improve the accuracy choose the value of R2 = 100k this reduces the error by 0.17% and increases the resistor program current by 12A. Since the LP2951 typically draws 60A at no load with Pin 2 opencircuited this is a small price to pay
REDUCING OUTPUT NOISE
It may be an advantage to reduce the AC noise present at the output. One way is to reduce the regulator bandwidth by increasing the size of the output capacitor. This is the only way that noise can be reduced on the 3 lead AS2954 but is relatively inefficient, as increasing the capacitor from 1F to 220F only decreases the noise from 430V to 160V rms for a 100kHz bandwidth at 5V output. Noise could also be reduced fourfold by a bypass capacitor across R1, since it reduces the high frequency gain from 4 to unity. Pick CBYPASS 1 / 2R1 x 200 Hz or choose 0.01F. When doing this, the output capacitor must be increased to 3.3F to maintain stability. These changes reduce the output noise from 430V to 100VRMS for a 100kHz bandwidth at 5V output. With the bypass capacitor added, noise no longer scales with output voltage so that improvements are more dramatic at higher output voltages.
HEATSINK REQUIREMENTS
Depending on the maximum ambient temperature and maximum power dissipation a heatsink may be required with the AS2954. The junction temperature range has to be within the range specified under Absolute Maximum Ratings under all possible operating conditions. To find out if a heatsink is required, the maximum power dissipation of the device needs to be calculated. This is the maximum specific AC voltage that must be taken into consideration at input. Figure 3 shows the condition and power dissipation which should be calculated with the following formula: PTOTAL = (VIN - 5) IL + (VIN)IG Next step is to calculate the temperature rise TR (MAX). TJ (MAX) maximum allowable junction temperature, TA (MAX) maximum ambient temperature : TR (MAX) = TJ (MAX) - TA (MAX) Junction to ambient thermal resistance (j-A) can be calculated after determining of PTOTAL & TR (MAX): (J-A) = TR (max)/P(MAX) If the (J-A) is 60C/W or higher, the device could be operated without a heatsink. If the value is below 60C/W then the heatsink is required and the thermal resistance of the heatsink can be calculated by the following formula, (J-C) junction to case, (C-H) case to heatsink, (H-A) heatsink to ambient: (J-A) = (J-C) + (C-H) + (H-A)
I IN= I L+ I G
IIN VIN IN OUT
5V IL
AS2954
+ GND + 2.2 uF
LOAD
IG
Figure 3. 5V Regulator Circuit
Rev.9/29/00
AS2954
TYPICAL APPLICATIONS
+VIN
8
ERROR OUTPUT
5
______ ERROR
+VIN VOUT
1
*VOUT = VIN
AS2954
SHUTDOWN INPUT
3
SD GND
4
FB
7
*MINIMUM INPUT-OUTPUT VOLTAGE RANGES FROM 4mV TO 400mV. DEPENDING ON LOAD CURRENT. CURRENT LIMIT IS TYPICALLY 160mA
Wide Input Voltage Range Current Limited
+V IN
+V IN V OUT *V
OUT =
5V
AS2954
GND
4
+
10uF
AS2954 FIXED +5V REGULATOR
Rev.9/29/00

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